1. Field of the Invention
The present invention relates to an improved machine vision camera and video preprocessing system which receives electromagnetic radiation from a field of view, selectively compresses the dynamic range of the image, and processes the image to remove the effects of camera jitter to provide an output adapted for a machine vision system.
2. Description of the Related Art
A current area of research involves interpreting video images through image processing or "machine vision." This technique uses specialized image processing hardware and software to analyze a received image and extract the information needed for control and/or surveillance. In spite of major efforts to develop machine vision systems for different applications, workable, cost effective devices having the capabilities and performance required for practical applications have been elusive.
One area of research has involved providing a clear image to the machine vision processing system during varying weather and visibility conditions. For example, conventional machine vision systems which receive electromagnetic radiation from a preset frequency range in the EM spectrum do not operate well when visibility conditions are such that reception of this preset frequency range does not produce a clear image. Therefore, an improved camera system is desired which produces a clear image during all visibility and weather conditions.
Another aspect of machine vision systems regards the necessity for real-time processing and the large amounts of information that must be processed. The information in the scene within the camera's field of view may have a wide dynamic range equivalent to a large number of bits of resolution. Conventional linear sampling requires many bits of resolution to accommodate this extensive dynamic range while also providing the granularity or detail of information required of the system. Due to the difficulties in processing such large amounts of information, various techniques have been used to select the most useful portion of the dynamic range of the image and thus reduce the amount of information that must be processed. One technique involves merely clipping off some portion of the dynamic range of the image, either the top or bottom brightness levels of the image, to reduce the amount of information that must be processed. However, this technique may present problems because important information may be lost. Therefore, a method and apparatus is desired which selectively compresses the dynamic range of the respective pixel values comprising an image to extract the most useful information from the extended dynamic range of the image.
Another problem associated with the use of machine vision systems has been environmentally induced motion in the camera system. When a camera is attached to an imperfectly rigid structure or is incorporated into a machine, the camera will inevitably be subject to various vibrations and jitter. This camera motion results in apparent motion in stationary portions of the image. This jitter, while not causing problems to humans, creates difficulties in a machine vision system in attempting to detect and track objects within its field of view. Therefore, an improved method and apparatus is desired which is capable of removing the jitter caused by the instability of the camera system.
For background on motion analysis in machine vision systems, please see Mallot et al., "Inverse perspective mapping simplifies optical flow computation and obstacle detection," Biological Cybernetics Vol. 64 (1991), pp. 177-185. The Mallot reference teaches computation of localized motion from successive video images. The method taught in Mallot is not concerned with, and is unsuitable for, determining a global motion component representing displacement between successive images.